The major goals of this core are: 1) to compare the utilities of interphase FISH, hypermetaphase FISH, and RT-PCR in their abilities to predict prognosis, monitor therapy responses, and predict relapse, and 2) to support the gene mapping studies needed for Dr. Lalitha Nagarajan to define the critical regions on chromosome 7 that are responsible for poor prognosis of 7q- patients. This core will perform 1) FISH on interphase nuclei to detect leukemic cells with chromosomal translocations such as t(15;17) and t(9;22), 2) develop interphase probes for inv (16) and t(8;21) in collaboration with Drs. Siciliano, Claxton and Chang, and develop interphase probes for 5q- and 7q- in collaboration with Dr. Nagarajan to correlate iFISH results with hypermetaphase FISH (HMF) and RT-PCR to support the FISH studies needed for gene mapping on chromosome 7 to define the critical regions on this chromosome that are responsible for poor prognosis (Dr. Lalitha Nagarajan). This core will collaborate with Dr. Elihu Estey to monitor therapy responses, Dr. Richard Champlin to monitor responses to BMT, Dr. Christopher Reading to enrich diploid stem cells, correlate iFISH, HMF, and RT-PCR, and Dr. Lalitha Nagarajan to map the critical regions on chromosome 7 that are responsible for poor prognosis.